The Airy beam has attracted significant interest from the optics community, thanks to its peculiar curved propagating trajectory and non-diffracting and self-healing features. In recent years, many researchers have investigated the physics of this unique beam and explored its wealth of potential applications, which range from improving microscopy and the optical manipulation of particles to nonlinear frequency conversion and the generation of light bullets.

Airy beams are usually generated by passing a Gaussian beam emitted from a conventional laser through a phase mask, which imparts a cubic phase modulation across the beam. Now, having developed a method for realizing laser beams with arbitrary beam profiles, Gil Porat and co-workers from Tel Aviv University in Israel have built a solid-state laser whose emitted beam has a two-dimensional Airy intensity profile (Opt. Lett. 36, 4119–4121; 2011).

The key to the development is the use of an aperiodic binary reflection diffraction grating as the output mirror of a laser cavity. The grating reflects most of the light back into the cavity but allows some to leave via various diffraction orders. The diffraction grating therefore serves the role of the phase mask normally used for Airy beam generation, except that it is now an integral part of the laser.

Credit: © 2011 OSA

The researchers fabricated a custom-designed silver-coated silicon grating using electron-beam writing to impose a transverse cubic phase, which is required to generate the Airy beam, on the diffracted light leaving the laser. The 70-nm-thick silver layer featured modulation patterns with a ridge height of 61 nm and provided a zero-order reflectivity of 87.6% and diffraction efficiency of 5% for each of the two first-order diffraction beams at a wavelength of 1,064 nm.

The researchers placed the grating in an optical cavity formed by an 808 nm diode-pumped Nd:YAG laser system, giving a total cavity length of 76 mm. They then passed one of the first-order diffraction beams from the grating through a lens to form the optical Fourier transformation of the beam at the plane of the diffraction grating. The lasing threshold pump power was 1.4 W and the slope efficiency was 13.5%, which corresponds to a maximum output power of 67.5 mW at a pump power of 1.94 W. To verify that the output beam from the laser was indeed an Airy beam, the team successfully performed a simple self-healing experiment in which a knife was used to block the main lobe of the beam.

The researchers say that their approach is more compact and convenient than the conventional method of generating Airy beams, which requires a phase-modulating element to be present outside the laser cavity. They also point out that the Airy beam laser is a proof-of-principle demonstration of a more general method currently under development that should also make it possible to build lasers and optical parametric oscillators capable of producing vortex beams and Bessel beams, or even beams with dynamically controllable and arbitrary profiles.